1. Fort RoupelSidirokastro Fort Roupel is a fortress at the north border of Central Macedonia, Greece, built in 1914. It became part of the fortifications of the Metaxas Line in the 1930s and became famous for its defence during the German invasion of Greece in April 1941. The Rupel fortifications are not far from the Serres-Promachonas national road, which leads to the Greek-Bulgarian border. They are just a short distance from the border in the narrow Rupel Gorge, through which the Strymon River flows. This place is of strategic importance for entry to Greek or Bulgarian territory and was fortified in 1914. During World War I, on 25 May 1916, the royal Greek government permitted the surrender of the fortress to the Germans and their Bulgarian allies. The German-Bulgarian troops then proceeded to occupy most of eas... From Wikipedia, the free encyclopedia.